Experimental pH advance control of the cheese whey batch kefir-type drink production with manipulated base flowrate

The pH control of cheese whey, glucose, grape juice and milk mixture fermentation with kefir yeast was investigated in a batch bioreactor where the kefir-type drink as a product different from the ones in the literature was obtained. The pH value of mixture in a bioreactor must not decrease under a certain value to avoid coagulation. The decrease in pH necessitates control application. The bioprocess was simulated with a Controlled AutoReggressive Integrated Moving Average (CARIMA) model for control purposes. The pH and sodium bicarbonate flow rate are selected as output and manipulated variable, respectively. Model parameter evaluation is achieved by using the U-D factorisation and a pseudo-random binary sequence (PRBS). The PRBS signal was given to 0.5 M sodium bicarbonate (NaHCO3) incoming flow rate, the system dynamic response data was obtained from the on-line pH monitor. The experimental pH control was achieved for the first time by using GPC (Generalized Predictive Control) system. The best control tuning parameter values were chosen according to performance criteria. According to the assessment of the experimental results, it was seen that the best control of the system without acid input was done with weighting factor, lambda=1. The analytical and microbiological data obtained from the kefir-type drink produced were evaluated according to Turkish Food Codex on Fermented Milk Products. Accordingly, it was counted the protein content of 100 ml as 3.11 +/- 0.10, the numbers of Laktobasillus as 9.44 +/- 0.38, the numbers of Laktococcus as 9.03 +/- 0.51 and the number of yeast as 9.99 +/- 0.70.